Calculating the Myoglobin-to-CK Ratio
The myoglobin-to-CK ratio is calculated by dividing the serum myoglobin concentration (ng/mL) by the total creatine kinase activity (U/L), yielding a unitless ratio.
The Calculation Formula
- Myoglobin-to-CK Ratio = Myoglobin (ng/mL) ÷ Total CK (U/L) 1
- Both values should be obtained from the same blood sample, ideally at hospital admission or emergency department presentation 1
- The ratio is expressed as a decimal value (e.g., 0.20,0.48) 1
Clinical Context and Interpretation
This ratio has emerged as a superior predictor of acute kidney injury (AKI) in rhabdomyolysis compared to either biomarker alone. 1
Key Thresholds for AKI Risk Stratification
- A ratio ≥0.48 indicates high risk for AKI with 79% sensitivity and 82% specificity 1
- A ratio ≥0.20 begins to indicate elevated AKI risk based on quartile analysis 1
- In the highest ratio quartile, 72% of patients developed AKI 1
Combined Risk Assessment Strategy
For optimal AKI prediction in rhabdomyolysis, combine the myoglobin-to-CK ratio with absolute myoglobin levels:
- High-risk criteria: Myoglobin-to-CK ratio ≥0.48 OR myoglobin ≥4,489 ng/mL 1
- This combined approach achieves 89% sensitivity and 92% negative predictive value for AKI 1
- The ratio outperforms CK alone (AUC 0.84 vs 0.31) and myoglobin alone (AUC 0.84 vs 0.73) 1
Important Clinical Caveats
- CK alone is a weak predictor of AKI in rhabdomyolysis (AUC only 0.31), despite being the traditional biomarker 1
- The ratio should be calculated from admission values for early risk stratification 1
- Both myoglobin and CK must be measured simultaneously from the same specimen to ensure accuracy 1
- This ratio is specifically validated for AKI prediction in rhabdomyolysis patients with CK ≥5,000 U/L and/or myoglobin ≥1,000 ng/mL 1